1. Field of the Invention
This invention relates to a toner, a fixing device, and an image forming apparatus.
2. Description of the Prior Art
There are known various electrophotographic methods. In general, such electrophotographic methods include a step for forming an electrostatic latent image on a photoreceptor by any means utilizing a photoconductive material (that is, an exposure step), a step for developing the latent image by the use of a toner to form a toner image, a step for transferring the toner image onto a transfer material (recording medium) such as paper, and a step for fixing the toner image by, for example, heating using a fixing roller.
The toner for use in such electrophotographic methods is generally composed of a material containing a resin as a main component (hereinafter, also simply referred to as a “resin”) and a coloring agent.
As for the resin constituting the toner, polyester resin is widely used, because polyester resin has a feature in that it facilitates the control of various properties of a resultant toner (that is, a toner finally obtained), such as elastic modulus, chargeability, and the like.
Further, such polyester resin is composed of a diol component. As for the diol component, aromatic diol such as bisphenol A has been commonly used (see Japanese Patent Laid-open No. Sho 57-109825 (page 1, lines 1 to 27), for example).
However, since polyester composed of such a diol component has a relatively large coefficient of friction and poor mechanical strength (that is, poor resistance to mechanical stress), obtained toner particles are liable to be fractured in a developing device, thus resulting in a case that problems such as poor electrification, contamination of the device, lowering in a fixing property, and the like occur.
Also, there is known a toner which is manufactured using polyester composed of aliphatic diol instead of aromatic diol such as bisphenol A (see Japanese Patent Laid-open No. 2001-324832 (page 2, lines 1 to 13), for example). In such a toner, a polyester block copolymer, which contains in its molecule a block obtained by condensation of aliphatic diol with carboxylic acids and a polyester block obtained by condensation of alicyclic diol with carboxylic acids, is used as polyester resin. However, a problem exists with such a toner in that a temperature range in which a sufficient fixing property (fixing strength) is ensured is narrow.